libbuxton: use wrapper functions for get_name() and get_group()

Some API functions are useful for both public and private code;
buxton_get_group() and buxton_get_name() are two examples.

Since private code should not be using the public API, make these two
functions wrappers for internal equivalents.

Also, use get_group() and get_name() where appropriate.
build: cleanups for libbuxton linkage

Both bt-daemon and libbuxton-security no longer use the public
libbuxton API, so remove the linkage.
test: Reorder daemon fork to test in parent

To keep consistent with check_buxton tests, have the function calls
that are being tested be run in the parent not the child.
test: Fix missing test coverage

Because _exit (2) does not seem to call the statistic gathering
cleanup code gcc embeds buxton coverage was not being gathered after
forking. Fix this by moving to exit (3) which does not break make
check thankfully.
test: Add tests for client notification
daemon: fix client Smack label handling

The fgetxattr() call here is for the client sockfd on the server, so the
Smack label returned is not the one we need. In fact, it label value
appears to be floor regardless of the label bt-daemon runs with.

To fix the issue, we need the actual label from the client end of the
socket, found in the SO_PEERSEC option value for the client sockfd.
smack: check for smackfs first

When Smack support is not enabled, a valid SMACK_LOAD_FILE is not
sufficient to track Smack support in bt-daemon, since SMACK_LOAD_FILE is
redefined to test/test.load2 for tests.

Instead, check the absolute directory of the smackfs first, and set
'have_smack' appropriately.
smack: add accessor for Smack state

Use the accessor for one of the test cases that fails when Smack is not
enabled on the system.
smack: fix logic error in smackfs checking

If the stat(2) call returns -1, we shouldn't check buf at all due to the
error. If it returns 0, then proceed to verify that it is a directory.
test: fix line endings in test.load2
test: add more Smack rules to test.load2

These three rules are currently being used in Tizen, and they will be
used in forthcoming tests.
test: add test for checking key labels
test: add smack tests for invalid subject/object
test: add new source file for Smack tests

Since there is already one test that requires a Smack-enabled host, and
many more tests need to be added specifically for Smack, move the
existing test case into a new test file, "check_smack", and add stubs
for using bt-daemon in the remaining tests.
test: Add identify client test
test: Add test for add_pollfd
test: Add test for deleting pollfds
test: Correct uid for client
core: Add signal handler to cleanup on INT and TERM
shared: Add workaround for client notification support

Because client's won't be notified synchronously but we'll need more
work in libbuxton to support client's polling for notifications, add
temporary support for notification messages through
buxton_wire_get_response.